The proteoglycans present in porcine and rat follicular fluid have been characterized with regard to their chemical and physical-chemical properties. The proteoglycans, approximately 2 million molecular weight, consist of 20% protein, 55% dermatan sulfate and 20% oligosaccharides. The protein core, approximately 400,000 molecular weight, has significantly different amino acid composition and susceptibility to various proteolytic enzymes from those of cartilage-type proteoglycans. The dermatan sulfate chains are approximately 56,000 in molecular weight, and iduronic acid accounts for 9% of total hexuronic acid. The oligosaccharides, approximately 350 chains per molecule, consist of penta and hexasaccharides, and are linked to the protein core by the O-glycosidic bonds. The chemical composition of these oligosaccharides has been determined. The oligosaccharides resemble those found in mucin-type glycoproteins. There is no apparent change in proteoglycan molecules with the size of follicles. Further, we have demonstrated that in vitro cultured granulosa cells produce several species of proteoglycans in addition to those found in porcine follicular fluid.